A spinal implant manufacturer switched from a metal trial to a PEEK trial insert in 2023 and cut intra-operative X-ray time by 40%. The PEEK part was radiolucent — invisible under fluoroscopy — so the surgeon could see the surrounding bone and the actual implant placement without the trial obscuring the view. The trial insert itself cost $90 to machine; the operating-room time it saved paid for itself in the first 20 cases.
That kind of outcome is why PEEK CNC machining has moved from a niche aerospace material to a mainstream engineering thermoplastic. PEEK (polyetheretherketone) is a high-performance semi-crystalline polymer that machines well, holds tight tolerances, survives autoclave sterilization, resists most chemicals, and weighs roughly one-eighth of aluminum. The trade-offs are real — it costs more than most plastics and demands clean tooling to avoid contamination — but for medical implants, aerospace brackets, semiconductor wafer carriers and a growing list of consumer-electronics applications, PEEK is the right answer.
This guide explains what PEEK is, how it machines, what tolerances and surface finishes it can hold, where it makes sense to specify it, and what to ask a CNC shop before you order. The advice is grounded in 23+ years of precision manufacturing at Ruijin Fenghui in Dongguan — a shop that holds IATF 16949, ISO 9001:2015 and ISO 13485 and runs 200+ CNC machines.
What Is PEEK?
PEEK is a semi-crystalline thermoplastic in the polyaryletherketone (PAEK) family. It was commercialized by ICI in the early 1980s and is now sold under several trade names (Victrex PEEK is the most common, followed by Solvay's KetaSpire and Evonik's Vestakeep). The base resin is FDA-cleared for food contact and is biocompatible per ISO 10993 for many medical applications.
Three grades dominate the CNC machining market:
- Unfilled PEEK — natural (tan/beige) color, the most common grade. Good all-around mechanical performance.
- Glass-filled PEEK (PEEK-GF30) — 30% glass fiber by weight. Higher stiffness, better dimensional stability, lower thermal expansion. Darker brown/black color.
- Carbon-filled PEEK (PEEK-CF30) — 30% carbon fiber. Even higher stiffness, better wear resistance, lower density, ESD-safe (electrically dissipative). Black color.
There are also medical-grade, food-grade and aerospace-qualified variants. The medical-grade versions come with full traceability and biocompatibility documentation per ISO 10993; aerospace variants come with batch certifications and meet specific flammability, smoke and toxicity requirements (e.g. FAR 25.853).
Key Properties of PEEK
| Property | PEEK (unfilled) | PEEK-GF30 | Aluminum 6061 (for comparison) |
|---|---|---|---|
| Density | 1.30 g/cm³ | 1.51 g/cm³ | 2.70 g/cm³ |
| Tensile strength | 100 MPa | 155 MPa | 310 MPa |
| Young's modulus | 3.6 GPa | 10 GPa | 69 GPa |
| Continuous use temperature | 260 °C | 260 °C | 200 °C (6061-T6) |
| Melting point | 343 °C | 343 °C | 582–652 °C |
| Coefficient of thermal expansion | 45 × 10⁻⁶ /°C | 20 × 10⁻⁶ /°C | 23 × 10⁻⁶ /°C |
| Water absorption (24h) | 0.5% | 0.3% | none |
| Chemical resistance | Excellent (except strong acids) | Excellent | Good |
| Radiolucency (X-ray visibility) | Yes (radiolucent) | Slightly visible | No (radiopaque) |
The two numbers worth highlighting for design decisions: continuous use temperature of 260 °C (PEEK keeps its mechanical properties in steam-sterilized autoclaves and hot-oil environments where most plastics fail) and Young's modulus of 3.6 GPa (about 20× lower than aluminum, which is why PEEK is never used where stiffness is the limiting factor — but is ideal where you want a part to flex without breaking, like a spinal fusion cage or a vibration-isolating bracket).
How to CNC Machine PEEK
PEEK machines well, but it is not aluminum. The biggest mistakes buyers and shops make are: running the same speeds and feeds as aluminum (PEEK needs slower spindle speeds, higher feed-per-tooth, and sharper tools), and using coolant that contaminates medical or food-grade parts.
Tooling
- Carbide tools are standard. Diamond-coated or polished-flute tools extend tool life on glass- and carbon-filled grades.
- Sharp edges only. A 0.05 mm wear land on the cutting edge doubles the heat generated and starts to melt the cut surface, producing a gummy, smeared finish.
- High-flute tools for finishing (4+ flutes for finishing, 2 flutes for roughing). PEEK chips are stringy; you need flute volume to clear them.
- Single-point turning uses ground carbide inserts with positive rake and a sharp edge. Avoid honed edges.
Speeds, feeds and chip control
- Spindle speed for milling: 3,000–6,000 RPM for Ø6–Ø12 mm cutters (vs 10,000+ RPM for aluminum). Reduce by 30% for filled grades.
- Feed per tooth: 0.05–0.15 mm/tooth (vs 0.04–0.08 mm/tooth for aluminum — PEEK likes higher chip loads to avoid rubbing).
- Depth of cut: 0.5–2× the cutter diameter for roughing; 0.05–0.2 mm for finishing.
- Chip evacuation: use air blast or vacuum, not flood coolant, when surface cleanliness matters. Flood coolant works for industrial parts but introduces contamination risk for medical and semiconductor.
Coolant and cleanliness
PEEK can be machined dry, with air blast, with cutting fluid (MQL), or with flood coolant — but the choice matters for the application. Medical implants and semiconductor parts need dedicated tooling and clean machining environments to avoid metal-particle contamination. For these parts, we machine PEEK on a separate cell with non-ferrous-only tooling, vacuum extraction, and a documented cleaning process before packaging. See our CNC machining materials guide for how we approach material-specific process control.
Stress relief and annealing
Machining stresses in PEEK can cause dimensional drift over hours or days — particularly in parts with thin walls or asymmetric geometry. For tight-tolerance parts, an annealing step at 200–250 °C for 1–4 hours after roughing (and again after semi-finishing if multiple setups are involved) brings the part to a stable, stress-relieved condition before final machining. For ultra-precision parts (below ±0.02 mm), we hold inventory for 24 hours post-machining before final inspection.
Tolerances and Surface Finish for PEEK
PEEK holds tolerance comparable to aluminum when machined with sharp tools and stable fixturing. The numbers below are what Ruijin holds in production in our Dongguan facility.
| Feature | Standard tolerance | Tight tolerance (achievable) | Notes |
|---|---|---|---|
| Milled dimensions | ±0.05 mm | ±0.02 mm | Stress relief recommended for tight |
| Turned dimensions | ±0.05 mm | ±0.02 mm | Single-point turning holds tighter |
| Hole diameter (drilled) | ±0.05 mm | ±0.02 mm | Drill + ream for tight |
| Thread (M3 and up) | Standard metric | Standard metric | PEEK taps cleanly with standard taps |
| Flatness | ±0.05 mm / 100 mm | ±0.02 mm / 100 mm | Stress-relieve before finish cut |
| Surface finish (as-machined) | Ra 0.8–1.6 µm | Ra 0.4 µm | Single-point turning gives smoother finish |
Two notes that matter for buyers. First, PEEK is hygroscopic — it absorbs 0.5% water by weight at saturation. Dimensional change from dry-as-machined to conditioned can be 0.1–0.2% in the first 48 hours. If your part is going into a humid or aqueous environment and you need a specific final dimension, machine 0.1–0.2% oversize and let the part condition before final inspection or finishing.
Second, PEEK's thermal expansion (45 × 10⁻⁶ /°C unfilled, 20 × 10⁻⁶ /°C filled) is real but rarely a problem for parts that operate near room temperature. For parts that see temperature swings of 50 °C or more, the filled grades (especially carbon-filled) behave much more like metal. For deeper tolerance physics, see our CNC machining tolerances guide.
Common Applications for PEEK CNC Parts
Medical devices
PEEK dominates spinal interbody cages, trauma trial sizers, surgical instrument handles and dental prosthetics. Radiolucency makes it ideal for implant trials (the surgeon sees bone, not metal). Biocompatibility per ISO 10993 makes it safe for limited-duration body contact. Sterilization by autoclave (134 °C steam), gamma irradiation and EtO all work without degrading the material.
Aerospace
PEEK replaces aluminum and titanium in brackets, clips and structural components where weight, fatigue and fire resistance all matter. Airbus and Boeing have qualified PEEK (and the lower-cost PEKK) for cabin interior brackets, wire harness clamps and high-temperature ducts. PEEK-CF30 is the typical aerospace grade — carbon fiber gives it higher modulus and ESD safety.
Semiconductor
PEEK and PEEK-CF30 are the dominant materials for wafer carriers, chip handling trays and vacuum chuck components. Static-dissipative carbon-filled grades prevent ESD damage; high purity (low extractables, low metal ion content) prevents wafer contamination.
Industrial and automotive
PEEK replaces metal in pump housings, valve seats, bearing cages and compressor components where chemical resistance, wear and temperature matter. Automotive applications include transmission seal rings, thrust washers and E-motor components.
Consumer electronics
PEEK is increasingly used in wearables, headphones and consumer electronics where strength-to-weight, RF transparency, and cosmetic finish matter. It is the same family of application our audio CNC line serves — see our TWS headset shell machining guide for a related case study.
How to Specify PEEK in Your RFQ
A clean PEEK RFQ should include:
- Material grade: e.g. "Victrex 450G unfilled" or "PEEK-CF30 (Solvay KetaSpire KT-820 CF30)". Generic "PEEK" without grade is a red flag.
- Application context: medical (Class Class I/II/III), aerospace, semiconductor, industrial, consumer. This drives cleanliness, traceability and documentation requirements.
- Required documentation: mill certificate (lot traceable), biocompatibility letter (for medical), FDA-grade statement (for food contact), REACH/RoHS (for EU).
- Tolerance and finish: per the table above, with explicit callouts on critical dimensions.
- Quantity: prototype, validation, production. PEEK raw material MOQ may apply.
- Cleanliness: cleanroom packaging, deionized water rinse, vacuum-bag sealing — whatever the application needs.
Red flags: a supplier who says "we can machine PEEK" but cannot name a specific resin grade; a supplier who quotes lead time for filled PEEK at the same numbers as unfilled (filled grades have longer raw material lead times); a supplier who cannot document lot traceability for medical-grade material. See our CNC supplier selection guide for the broader supplier qualification checklist.
Conclusion
PEEK is the right material when you need a polymer that survives 260 °C, autoclaves, aggressive chemicals, and demanding mechanical fatigue — and you want to machine it with the same dimensional precision you get from aluminum. The trade-offs are real (cost, machinability nuances, contamination control) but for medical implants, aerospace brackets, semiconductor carriers and a growing list of consumer-electronics applications, PEEK is the right call.
Ruijin Fenghui Precision Technology has been machining PEEK parts — along with metal CNC components for audio, automotive, medical, drone and robotics applications — for 23+ years out of our Dongguan facility. We hold IATF 16949, ISO 9001:2015 and ISO 13485, run 200+ CNC machines, and machine PEEK in a dedicated clean cell with non-ferrous tooling. Send your STEP file and drawing and we will return a DFM review and a quote within 24 hours.
Need a CNC machining quote for PEEK parts? Send your STEP file and drawing — free DFM review and a firm quote within 24 hours.